guidelines for creating IGES geometry

[mihaipruna]

Hello Elmer forums! This is my first post here
Based on an example I saw, I assumed that by creating an iges file, where the solid represents say the fluid, and a cutout represents a solid immersed in the fluid, it would automesh the domain for you.
I tried a box where I cut half a sphere on one side, with the intent of using a symmetry constraint on those boundaries.
But it gave me some errors while importing the geometry and then the GUI crashed.

Leaving two solids in the Iges file, it doesn't work as intended, as a sphere immersed in the box is not automatically detected so it's assumed as part of body1.
I'm using Autodesk 123D to create the Iges files. I'd like to see some examples,tips or workflows for creating geometry for CFD analysis.
Thanks!

[raback]

Hi

Unfortunately the build-in CAD interface of Elmer is limited to one body. Often complex meshes are created outside ElmerGUI. There are lengthy discussions on using Gmsh, netgen, Salome etc. for the meshing of CAD geometries. This is clearly a problem at the current workflow. ElmerSolver itself does not have any restrictions for multibody systems.

-Peter

[mihaipruna]

Hi Peter, thanks for the response.
Even one body would be enough as I can make a cut to represent the solid inside and assign wall conditions on the surfaces of the cut.
But, like I said, it crashed when I tried that with a sphere.

[studioa]

Mihai -
there are lots of proprietary software packages that can generate and prepare meshes for CFD.

On the other hand, you can go with the Open Source and do similar things.

Here are couple Open Source packages that are available and come into my mind right now:

To generate the mesh: FreeCAD, Blender, MeshLab, OpenFlipper, Salome.

Then you can export the mesh from these packages and prepare the mesh for CFD:

NetGen w/ NGSolve (very fast) or EnGrid (slower). NetGen has an Elmer exporter that works fantastic.

Then once you have the mesh prepared, you can import into Elmer and apply bc, solvers, etc. and run the simulations.

Finally you can use either Elmer Post to visualize or ParaView (which I use most f the time) or VisIt.

Hope this helps.

Adrian

[juxifeng]

Mihai -
there are lots of proprietary software packages that can generate and prepare meshes for CFD.

On the other hand, you can go with the Open Source and do similar things.

Here are couple Open Source packages that are available and come into my mind right now:

To generate the mesh: FreeCAD, Blender, MeshLab, OpenFlipper, Salome.

Then you can export the mesh from these packages and prepare the mesh for CFD:

NetGen w/ NGSolve (very fast) or EnGrid (slower). NetGen has an Elmer exporter that works fantastic.

Then once you have the mesh prepared, you can import into Elmer and apply bc, solvers, etc. and run the simulations.

Finally you can use either Elmer Post to visualize or ParaView (which I use most f the time) or VisIt.

Hope this helps.

Adrian

Hi Adrian,

I am also new Elmer, actually new to the CFD and FEA. My final intension is to do a FEA pressure analysis on a moving lens 'cylinder', which is an uni project.
I have created using freeCAD the cylinder geometry and saved as a file named len.fcstd.
Then, I am really struggling what to do next.
1. How can I create mash in freeCAD?
2. How do I export mash from freeCAD and prepare for meshes for Elmer?
3. How do I make velocity as a variable and find out the surface pressure distribution?
If you know these, please share with us!

Thanks,
Jin

[Chris_DE]

Hello Jin,

following your questions, I propose a way I would use in this case. (other ways do exist)

1. How can I create mash in freeCAD?

design only the geometry in Freecad and export it in step or iges format

2. How do I export mash from freeCAD and prepare for meshes for Elmer?

You can use FreeCAD and its Mesh module interface which proposes only basic mesh functions (the use of advanced mesh features require editing script). Its a question of taste...
I suggest rather to load the exported geometry in Gmsh to generate a mesh file. (Gmsh works also with interface and script, its script is quite easy to understand)

To generate the mesh, you should have a look to the tutorial I listed in your other post there viewtopic.php?f=4&p=6039#p6039

3. How do I make velocity as a variable and find out the surface pressure distribution?

I think that if you activate the Navier-Stockes solver in the equation window of ElmerGUI, it should activate the calculation of velocity field.

I hope I say no mistakes

Chris